May R M, Nowak M A
Department of Zoology, University of Oxford, U.K.
Proc Biol Sci. 1995 Aug 22;261(1361):209-15. doi: 10.1098/rspb.1995.0138.
Analyses of the selection pressures acting on parasite virulence are made more complicated when individual hosts can simultaneously harbour many different strains or genotypes of a parasite. Here we explore the evolutionary dynamics of host-parasite associations in which individual hosts can be coinfected with many different parasite strains. (We take coinfection to mean that each strain transmits at a rate unaffected by the presence of others in the same host.) This study thus represents the opposite extreme to our earlier work on superinfection in which there is a dominance hierarchy such that only the most virulent strain present in a host is transmitted. For highly diverse populations of parasite strains, we find that such coinfection leads to selection for strains whose virulence-levels lie in a relatively narrow band close to the maximum consistent with the parasite's basic preproductive ratio, R0, exceeding unity.
当单个宿主能够同时携带寄生虫的许多不同菌株或基因型时，分析作用于寄生虫毒力的选择压力会变得更加复杂。在这里，我们探讨宿主 - 寄生虫关联的进化动态，其中单个宿主可能会被许多不同的寄生虫菌株共同感染。（我们将共同感染定义为每个菌株的传播速率不受同一宿主中其他菌株存在的影响。）因此，这项研究代表了与我们早期关于重复感染的研究相反的极端情况，在重复感染中存在优势等级制度，以至于宿主中存在的最具毒力的菌株才会传播。对于高度多样化的寄生虫菌株群体，我们发现这种共同感染会导致对毒力水平处于相对狭窄范围内的菌株的选择，该范围接近与寄生虫的基本繁殖率R0超过1相一致的最大值。
